EKT212/4 Principles of Measurement and Instrumentation
(Sem2 2014/15)
Tutorial 2
Part 1:
(a) Explain with a circuit diagram the operation of a basic dc ammeter using PPMC
instrument.
(b) What the value of shunt resistance is required for using 50 µA meter movement having
an internal resistance of 250 Ω for measuring current in the range of 0-500 mA?
(c) Design a multirange ammeter with ranges of 0-1 A, 5 A, 25 A, 125 A employing
individual shunts for each range. A D’ Arsonval movement with an internal resistance of
730 Ω and a full scale current of 5 mA is available.
(d) Design an Ayrton shunt to provide an ammeter with current ranges of 0 -1 mA, 5 mA, 20
mA, and 50 mA, using a D’Arsonval movement having internal resistance of 50 Ω and a
full scale current of 100 µA.
(e) Figure 1 shows an Aryton shunt of an ammeter with a current range of 0 – 1 mA, 10 mA,
50 mA and 100 mA. A D’ Arsonval movement with an internal resistance of 100 Ω and
full scale current of 50 µA is used. Propose the value of Ra, Rb, Rc and Rd for this
design.
Figure 1
(f)
A current meter that has an internal resistance of 100 Ω is used to measure the current
through resistor Ra in Figure 2. Determine the percentage of error of the reading due to
ammeter insertion.
Figure 2
EKT212/4 Principles of Measurement and Instrumentation
(Sem2 2014/15)
Part 2:
Question 1
(a) Explain with a circuit diagram the operation of a basic dc voltmeter using PPMC
instrument.
(b) Define sensitivity of voltmeters. What is the significance of sensitivity in voltmeters?
(c) A basic D’Arsonval movement with a full scale deflection of 50µA and having an
internal resistance of 1800 Ω is available. It is to be converted into a 0 – 1V,0-5V, 020V, 0-100V multirange voltmeter using individual multipliers for each range. Calculate
the values of the individual resistor.
Question 2
(a) State the effect of using a voltmeter of low sensitivity.
(b) Convert a basic D’Arsonval movement with an internal resistance of 100 Ω and a full
scale deflection of 1mA into a multirange dc voltmeter with the voltage ranges of a 0 –
1V,0-10V, 0-50V.
Question 3
Figure 3
Two different voltmeters are used to measure the voltage across R2 in the circuit in Figure 3.
The meters are as follows:
(i)
5 V range, S = 20 kΩ/V.
(ii)
10 V range, S = 20 kΩ/V.
Let Vs = 40V, R1 = 20 kΩ, R2 = 1 kΩ and R3 = 10 kΩ. Identify which voltmeter introduces
least error due to loading.
EKT212/4 Principles of Measurement and Instrumentation
(Sem2 2014/15)
Question 4
Figure 4
(a) The circuit diagram of Figure 4 shows a full wave rectifier ac voltmeter. The meter
movement has an internal resistance of 250 Ω and required 1 mA for full scale
deflection. The diodes each have a forward resistance of 50 Ω and infinite reverse
resistance. Calculate:
(i) The ohms per volt rating of the ac voltmeter.
(ii) The series resistance required for full scale meter deflection when 25V rms is
applied to the meter terminals.
(b) Sketch the circuit and waveforms for an ac voltmeter using PMMC instrument and a
half wave rectifier. Explain the circuit operation.
(c) A D’Arsonval meter movement with a full scale deflection current rating 0f 1mA and
an internal resistance of 500Ω is to be used in a half wave rectifier ac voltmeter.
Calculate the ac and dc sensitivity and the value of the multiplier resistor for a
30Vrms range.
EKT212/4 Principles of Measurement and Instrumentation
(Sem2 2014/15)
Part 3:
(a) Explain with a circuit diagram the operation of a series type ohmmeter.
(b) A 1mA full scale deflection current meter movement is to be used as an ohmmeter
circuit. The meter movement has an internal resistance of 500 Ω and a 5V battery will
be used in the circuit. Mark off the meter face (dial) for reading resistance with a
20%, 50% and 100% deflection.
(c) With reference to Figure 5, state the ohmmeter scale when the current is 0A, 1/2 FSD,
1/4FSD and FSD
Figure 5